City-level livestock methane emissions in China from 2010 to 2020

Livestock constitute the world’s largest anthropogenic source of methane (CH4), providing high-protein food to humans but also causing notable climate risks. With rapid urbanization and increasing income levels in China, the livestock sector will face even higher emission pressures, which could jeopardize China’s carbon neutrality target. To formulate targeted methane reduction measures, it is crucial to estimate historical and current emissions on fine geographical scales, considering the high spatial heterogeneity and temporal variability of livestock emissions. However, there is currently a lack of time-series data on city-level livestock methane emissions in China, despite the flourishing livestock industry and large amount of meat consumed. In this study, we constructed a city-level livestock methane emission inventory with dynamic spatial-temporal emission factors considering biological, management, and environmental factors from 2010 to 2020 in China. This inventory could serve as a basic database for related research and future methane mitigation policy formulation, given the population boom and dietary changes.

Table S2.Dairy cattle manure management system ratio in different regions.
Table S3.Non-dairy cattle manure management system ratio in different regions.
Table S4.Sheep/Goat manure management system ratio in different regions.

Table S5. Methane conversion factors in different mean annual temperature (%).
Table S6.Average life span (ALS) of different livestock animals (month).

Table S8. Coefficients of variation of EFs of different livestock categories.
Table S9.Data sources of the main data in this study.) were all considered in the determination of ij GE according to IPCC 2019 and previous studies 1,2 .It is noted that the energy for pregnancy and lactation is just for mature females who give birth, and the growth is only for young animals.
The energy for maintenance ( m NE ) is the energy animals used to maintain their life, and is the function of body weight as follows.
0.75 , where i Cf is the coefficient varies over livestock categories math to the animal i , and the value of which refers to IPCC 2019 inventory guidelines 1 , and the weight is the body weight of the animal i in the year j .
The energy for animal activity ( a NE ) is net energy for activity, including obtaining food and etc.
the value of a NE is defined as a part of a NE as follows, S2 is for cattle and buffalo, and S3 is for sheep and goats.
where C is the coefficient determined by the feeding situation, and according to previous studies and the current situation of China's livestock breeding factor, Qinghai, Xinjiang, Tibet, and Inner Mongolia were mainly in the grazing system.The corresponding C value can be found in IPCC 2019 inventory guidelines 1 .
The energy for lactation ( l NE ) is only for mature female animals as follows, (1.47 0.4 ) where milk is the amount of milk production and the fat is the content of milk which all can be found in China diary yearbook 3 .
The energy for pregnancy ( p NE ) is also only for mature female animals as follows, the S5 is for non-dairy cattle and buffalo, S7 is for sheep and goats.
where c is the coefficient of 0.8, 1.0 and 1.2 for females, castrates and bulls, respectively, due to the data available, the mean value was adopted in this study.The m weight is the weight of the mature body of the certain animal, WG is the wright gain of young animals which can be measured as S6, the y weight is the body weight of the young animal, the m age and y age is the age of mature and young animals, respectively 2 .In S7, i BW is the bodyweight of animals at weaning, and f BW is at 1-year old with the unit of kg, due to lack of detailed information about sheep and goats, according to Xu's study, the value of WG was set as 0.15 kg, and the body weight at weaning and 1-year old was assumed is same to the weight of young and mature animals.Additionally, the value of a and b in S7 can be found in IPCC 2019 inventory guidelines 1

S8
where wool E is the energy value for sheep/goats to produce each kg of wool, which is 24 MJ kg -1 , and wool P is the wool production in a year per head (kg year -1 ) 1 .Due to the lack of specific wool production data, here we use the provincial level data through estimation combining the total wool production and the population of sheep/goats.

Table S10 .
The uncertainty interval of the final emission results.For comprehensively estimating the gross energy ( ij GE ) of large ruminants, including non-dairy cattle, dairy cattle, buffalo, sheep and goats.Energy for maintenance ( p NE ), energy for growth ( g NE ) and energy for producing wool ( wool NE . The energy for producing wool ( wool NE ) is the net energy required to produce wool in a year for sheep and goats, and the equation is as follows,

Table S1 .
Swine manure management system ratio in different regions.

Table S2 .
Dairy cattle manure management system ratio in different regions.

Table S3 .
Non-dairy cattle manure management system ratio in different regions.

Table S4 .
Sheep/Goat manure management system ratio in different regions.

Table S5 .
Methane conversion factors in different mean annual temperature (%).

Table S6 .
Average life span (ALS) of different livestock animals (month).

Table S7 .
Coefficients of variation of activity data among different dataset (city level, country level and international level).

Table S8 .
Coefficients of variation of EFs of different livestock categories.

Table S9 .
Data sources of the main data in this study.

Table S10 .
The uncertainty interval of the final emission results.